Controlling emissions in diesel engines has posed significant challenges to the automotive industry. Several different methods of controlling emissions from diesel engines have been proposed. One type of method is generally known as low temperature diesel combustion, and may be used to control the emissions of substances including but not limited to nitrogen oxides (“NOx”) and particulate matter.
One method of performing low temperature diesel combustion is to perform an early injection of fuel into the combustion chamber of the engine so that the fuel burns at lower temperatures. The lower combustion temperatures produce lower concentrations of NOx, particulate, and other byproducts.
The early injection of fuel allows the fuel to mix more thoroughly with air than ordinary diesel combustion, and is therefore sometimes referred to as “early homogenization combustion.” Likewise, ordinary diesel combustion may be referred to as “diffusion” combustion due to the fact that combustion occurs with comparatively less mixing of fuel and air in the combustion chamber before combustion begins. While early homogenization combustion may improve engine efficiency and decrease concentrations of NOx and particulate emissions, it may also lead to lower exhaust temperatures, which may negatively impact the performance of various aftertreatment devices, particularly when a diesel engine is operating at a light load and/or at idle.
The inventors herein have recognized that the reduction of NOx, particulate and other emissions from a diesel engine may be more efficiently addressed by utilizing an aftertreatment device in combination with a method of operating the engine that includes performing at least one combustion in the combustion chamber at a first intake valve closure timing, determining a temperature of the aftertreatment device, and if the temperature of the aftertreatment device is equal to or below a preselected temperature threshold, then performing at least one combustion in the combustion chamber at a second intake valve closure timing to thereby increase the temperature of exhaust emitted by the diesel engine. In some embodiments, the second intake valve closure timing may be later than the first intake valve closure timing. In yet other embodiments, an exhaust valve timing may be adjusted in combination with a late injection of fuel into the combustion chamber to produce higher exhaust temperatures.